Chapter 2

Question 1

Inner part of class consist of____

Answer 1

1. Fields- store date persistently w/i an object
2. Constructors- ensures that an object is set up properly when it is first created
3. Methods- implement the behavior of an object; provide its functionality

Question 2

What is another name for fields?

Answer 2

instance variables

Question 3

Field pattern

Answer 3

• usually start with reserved word: private
• they include a type name (such as int, String, Person, etc.)
• include a user-chosen name for the field variable
• end with semicolon

Question 4

Fields

Answer 4

• Store values for an object
• Define state of object
• Use inspect to view state
• some values change often
• some change raraely
• always define fields to be private
  ie:
  private int price;

Question 5

constructors

Answer 5

• initialize the fields
• have same name as class
• close association w/fields
• store initial values into the fields
• external parameters values for this

Question 6

For these constructors, why isn’t price set to 0?
{
price = cost;
balance = 0;
total = 0;
}

Answer 6

Because we don’t know what the ticket price will be for this project since it’s entered externally.

Question 7

Passing data via parameter

Answer 7

• parameters are another sort of variable
• used to hold data
• temporary messenger carrying data originating externally

Question 8

What is formal parameter vs actual parameter

Answer 8

formal is parameter names such as cost in
TicketMachine(int cost)
while actual is the user supplied value like 500 if user entered that

Question 9

Assignment

Answer 9

• values are stored into fields & other variables via assignment statements
  ie:
  variable = expression;
  price = cost;
• a variable stores a single value, so any previous value is lost
• types must match

Question 10

Methods

Answer 10

• yellow boxes
• 2 parts: header & body
• always has parenthesis and no semicolons at end

Question 11

method header

Answer 11

• provides method’s signature
• tells us:
  method name
  parameters it takes
  whether it returns a result
  it’s visibility to objects of other classes

Question 12

Method body

Answer 12

• Encloses the method’s statements with curly brackets
• contain:
  declarations- used to create additional, temp variable space
  statements- describe actions of the method
• a set of declarations and statements b/t curly brackets is a block

Question 13

Accessor (get) Method

Answer 13

• always has non void return type
• returns value (result) of the type given in header
• contains return statement

Question 14

T or F: returning is the same as printing

Answer 14

F: returning is not printing!

Question 15

Returning a value

Answer 15

• some info passed internally b/t 2 different parts of a program
• 1 part requested info from object via method call & return value is the way the object has of passing the info back to caller

Question 16

Mutator method

Answer 16

• Changes state of object- mutate
• achieved through changing the value of 1 or more fields
  typically contain assignment statements
  often receive parameters

Question 17

What kind of method is this code:
Public int getPrice()
{
return price;
}

Answer 17

Accessor

Question 18

What kind of method is this:
public void insertMoney (int amount)
{
balance = balance + amount;
}

Answer 18

mutator

Question 19

set mutator methods

Answer 19

• most basic
• fields often have dedicated set mutator methods
• simple distinctive form:
  void return type
  method name related to field name
  single parameter, w/same type as the type of the field
  single assignment statement

Question 20

Local variables

Answer 20

• similar to field variables
• never have “private” or public”
• lifetime is at method execution- created when method is called & destroyed when method finishes

Question 21

Local variable are defined within a method

Answer 21

• short lived like parameters
• the method sets their values- unlike parameters they do not receive external values
• used for temp calc and storage
• only accessible w/i the method

Question 22

What is this code doing?
int amountToRefund = balance;

Answer 22

declaring the variable amountToRefund and giving it an initial value
- it is common to initialize local variables W/I their declaration

Question 23

What is this?
int amountToRefund;

Answer 23

local variable

Question 24

What is the difference in scope between a local variable and field?

Answer 24

• A scope of a local variable is the block in which its declared while scope of fields is its whole class
• lifetime of LV is time of execution of the block in which its declared while lifetime of field if the lifetime of its containing object

Question 25

What are the different kinds of variables

Answer 25

fields
parameters
local variables

Question 26

T or F: Java keywords never contain uppercase letters

Answer 26

True

Question 27

Field pattern

Answer 27

• usually start with reserved word: private
• they include a type name (such as int, String, Person, etc.)
• include a user-chosen name for the field variable
• end with semicolon

Question 28

T or F: all fields are automatically initialized to a default value if they are not explicitly initialized

Answer 28

True
so integers are automatically set to 0

Question 29

Constructor space of the object (or method space for methods)

Answer 29

• Used to provide space to store the values for the constructor’s parameters.
• Created only when constructor executes

Question 30

What is scope?

Answer 30

• The section of source code from which the variable can be accessed
• scope of parameter is restricted to the body of the constructor/method in which it is declared
• scope of field is the whole class definition so it can be accessed from anywhere in the same class

Question 31

lifetime

Answer 31

• describes how long the variable continues to exist before it is destroyed
• lifetime of parameter is limited to a single call of a constructor/method
• lifetime of field is the same as lifetime of the object to which it belongs

Question 32

Effect of mutator

Answer 32

an object will often exhibit slightly different behavior before and after it is called

Question 33

What compound assignment operator is used when adding an amount to the value in a variable?

Answer 33

+=
balance + = amount;

Question 34

what is the basic form of a call to println?

Answer 34

System.out.println(something-we-want-to-print);

Question 35

What are the 3 components in this parameter?
System.out.println(“# “ + price + “ cents.”);

Answer 35

• the string literal: “# “ (note the space after the hash)
• the value of the price field (note that there are no quotes around the field name because we want the field’s value, not its name)
  -the string literal: “ cents.” ( note the space character before the word)

Question 36

_________ “+” is a string-concatenation operator

Answer 36

• when used between a string and anything else
• ie., it concatenate/joins strings together to create a new string

Question 37

Non-void vs void return type

Answer 37

-non-void: method will return some data to the place it was called from- and that data will be used in the caller for further calcs or program manipulations
-void: return nothing

Question 38

conditional statement

Answer 38

-Takes 1 of 2 possible actions based upon the result of a test.
-aka if-statements
-general form:
if(perform some test that gives a t/f result) {
Do the statements here if the test gave a true result
}
else {
Do the statements here if the test gave a false result
}

Question 39

Scope highlighting

Answer 39

colored boxes around some elements, such as methods and if-statements.

Question 40

T or F: Fields are used to store data that persist throughout the life of a method. As such, they maintain the current state of an object. They have a lifetime that lasts as long as their method lasts.

Answer 40

False: Fields are used to store data that persist throughout the life of an object. As such, they maintain the current state of an object. They have a lifetime that lasts as long as their object lasts.

Question 41

T or F: Formal parameters have a scope that is limited to their defining constructor or method.

Answer 41

True: Formal parameters have a scope that is limited to their defining constructor or method.

Question 42

T or F: Fields are defined inside constructors and methods.

Answer 42

False: Fields are defined outside constructors and methods.

Question 43

T or F: Java requires that every variable be given a type before it can be used.

Answer 43

True: Java requires that every variable be given a type before it can be used.